Year: 1969
Engine: 427ci 390hp
Transmission: Manual
Carburetor: QuadraJet 7029207

What ACDelco spark plug would you recommend? How about other brands (NGK?) Any other brands to look into?

 

Absolutely NGK. Delco stuff is outsourced. Not what it was years ago.

 

which NGK plug?

 

https://www.ngk.com/application/search

genuine site..

i went with the cheapest one for my 79

 

I’ve used ac, champion and recently switched to ngk, smoothest idle of the three, highly recommended.

72 LS5.

 

Do your heads use the tapered plug or the flat gasketed plug design? If you are absolutely sure your heads are original then they should be flat seat, gasket style. If replacement, they could well be the tapered style. Check what plugs are in your engine before ordering anything.

My '67 427/390 (flat seat style) uses NGK BPR4ES. These flat seats use a separate metal washer/gasket.
My '72 454/390 (tapered seat style) uses NGK UR-5. These tapered seats use no gasket at all.

The plug GM recommended for your '69 is a 43N (4=14mm thread, 3-heat range, N=extended reach, non-resistor). Many of us feel the 3 and 4 heat ranges are too cold for today's gas and the way we drive these cars. Delco's 5 heat is commonly recommended (R45XLS) unless you are racing or spending considerable driving time above 115 kph (~70mph).

NGK uses an opposite scale where instead of getting "hotter" with increasing numbers, NGK gets "hotter" with decreasing numbers. NGK 5 or 4 is roughly equivalent to Delco 5 or 5+.

You won't find any non-resistor plugs today except old-stock on eBay; all plugs appear to be resistor-type and carry the R designation.

 

That's what I noticed too....the only plug to buy IMO..

 

So what is the NGK equivalent of the R45XLS?

 

Sorry, I guess I wasn't clear. The equivalent is the BPR4ES, but you have to make sure the heads on your engine use the flat seat design.
Attached is the NGK cross-reference guide.

 

So if flat seat design: NGK 6578 (or 7222?) - BPR4ES
If tapered design: NGK 2771 - UR5

Correct?

 

I went with these for my 72 stock ls5.

 

If you look here BPR5ES for 1969 cast iron heads
https://ngk.mypartfinder.com/

 

Right, but he needs to make sure he has the '69 heads and not a later replacement of some sort.

Yes, though I'm not sure where the 6578 number came from and I don't see it in the catalog.

The 4 in BPR4ES or UR4 is a slightly hotter plug than their 5 (BPR5ES or UR5). I think for our uses it won't matter because as you can see in the catalog the equivalency to Delco's 5-heat range is mixed between the two.

 

https://www.ngk.com/ngk-6578-bpr4es-nickel-spark-plug
https://www.ngk.com/ngk-7222-bpr4es-nickel-spark-plug

what's the difference? it seems the 6578 is the newer version of the 7222

 

1969 is a high compression engine. You should be looking at the cooler BPR5ES assuming you have the stock heads
Have you removed a plug?

 

no i am taking it to the garage next week but i want to supply him the plugs myself so that I am sure he puts in the correct ones.

 

Can you see any markings on the current plugs for what brand and model they are? That would be easy to cross-reference so you are assured you get compatible replacements.

For gasket seat vs. taper seat, the hex portion of the spark plugs are significantly different sizes. Gasket plugs are 13/16" hexes while taper plugs are just 5/8".

I agree that the 5-heat plugs would be fine as well.

I see, yes, the 6578 is the replacement for the 7222.

 

So how are you going to determine that if you don't look at what is currently installed?